windbg - VB6 Debugging - compiled

Question

My scenario is I'm supporting a VB6 app at the place I work and in the last few weeks it has started crashing more often than it ever used to. It uses both a local Access MDB database and a remote SQL Server DB for different types of storage. The good news is we are writing a replacement app, the band news I need to support this one in the meantime and the vendor is long gone from this world.

What are some ways I could try and diagnose what is causing the crash? For example so far I've tried ODBC tracing (For the MDB component), SQL Profiler tracing and ProcMon on a client PC.

Is there anything else I could try to discover what the app was trying to do at the time of the crash?

Answer 1

You can also start in a debugger.

windbg or ntsd (ntsd is a console program and maybe installed). Both are also from Debugging Tools For Windows.

Download and install Debugging Tools for Windows

http://msdn.microsoft.com/en-us/windows/hardware/hh852363

Install the Windows SDK but just choose the debugging tools.

Create a folder called Symbols in C:

Start Windbg. File menu - Symbol File Path and enter

srv*C:symbols*http://msdl.microsoft.com/download/symbols

then

windbg -o -g -G c:windowssystem32cmd.exe /k batfile.bat

You can press F12 to stop it and kb will show the call stack (g continues the program). If there's errors it will also stop and show them.

Type lm to list loaded modules, x *!* to list the symbols and bp symbolname to set a breakpoint

Use db address (as in db 01244 to see what's at that memory.

If programming in VB6 then this environmental variable link=/pdb:none stores the symbols in the dll rather than seperate files. Make sure you compile the program with No Optimisations and tick the box for Create Symbolic Debug Info. Both on the Compile tab in the Project's Properties.